Typically, during semiconductor processing, a plasma etch process, for example a dry plasma etch process, is utilized to remove or etch material along fine lines or within vias or contacts patterned on a semiconductor substrate. The plasma etch process generally involves positioning a semiconductor substrate with an overlying patterned, protective layer, for example a photoresist layer, into a processing chamber and etching exposed areas of the substrate through the pattern.
Once the substrate is positioned within the chamber, it is etched by introducing an ionizable, dissociative gas mixture into the chamber at a pre-specified flow rate, while throttling a vacuum pump to achieve a processing pressure. Then, plasma is formed when a portion of the gas species is ionized by collisions with energetic electrons. The heated electrons dissociate some of the gas species in the gas mixture to create reactant species suitable for the exposed surface etch chemistry. Once the plasma is formed, any exposed surfaces of the substrate are etched by the plasma. The process is adjusted to achieve optimal conditions, including an appropriate concentration of desirable reactant and ion populations to more selectively etch various desired features (e.g., trenches, vias, contacts, etc.) in the exposed regions of substrate. The exposed regions of the substrate where etching is required are typically formed of materials such as silicon dioxide (SiO2), poly-silicon and silicon nitride, for example.
Conventionally, various techniques have been implemented for exciting a gas into plasma for the treatment of a substrate during such semiconductor device fabrication. In particular, capacitively coupled plasma (CCP) processing systems, such as parallel-plate systems, for example, or inductively coupled plasma (ICP) processing systems, have been utilized for plasma excitation. Among other types of plasma sources, there are microwave (MW) plasma sources, including those utilizing electron-cyclotron resonance (ECR), surface wave plasma (SWP) sources, and helicon plasma sources.
It is becoming common wisdom that SWP sources offer improved plasma processing performance, particularly for etching processes, over CCP systems, ICP systems and resonantly heated systems. This improved performance of SWP sources includes in general the production of a high degree of ionization at a relatively lower Boltzmann electron temperature (Te). In addition, SWP sources generally produce plasma richer in electronically excited molecular species with reduced molecular dissociation. However, the practical implementation of SWP sources still suffers from several deficiencies including, for example, plasma stability and uniformity, and electron temperature that is still higher than preferred.